1. Field of the Invention
The present invention relates to a center electrode assembly for use, for example, in an isolator, a circulator, or other suitable apparatus to be operated in a microwave band, a nonreciprocal circuit device, a communication device, and a method of producing such a center electrode assembly.
2. Description of the Related Art
A conventional center electrode assembly is described in Japanese Unexamined Patent Application Publication No. 5-37206. The center electrode assembly, as shown in FIG. 17, includes two parallel center electrodes 220a disposed on the upper surface 210a of a ferrite member 210 and the lower surface 210b of the ferrite member 210, using a thermosetting type electroconductive paste material or a firing (baking) type conductive paste material according to a screen printing method. An insulation layer 230 is formed on the upper surface 210a and the lower surface 210b of the ferrite member 210 by screen printing. In this way, the center electrodes 220a and insulation layers 230 are alternately formed. Connecting electrodes 220b are formed on the peripheral side-surface 210c of the ferrite 210 by screen printing. The ends of the connecting electrodes 220b are connected to the ends of the center electrodes 220a, respectively.
Thus, a center conductor 220 is formed, in which three center electrodes 220a are disposed on the upper surface 210a and the lower surface 210b of the ferrite member 210 so as to intersect each other in their insulation state, and the ends of each of the center electrodes 220a are connected to each other through the connecting electrodes 220b. That is, on the upper and lower surfaces 210a and 210b of the ferrite member, center electrodes 220a defining a first layer, a first insulation layer 230, second center electrodes 220a defining a second layer, a second insulation layer 230, and center electrodes 220a defining a third layer are laminated by a screen printing method, respectively. The center electrodes 220a defining the third layer are arranged so as to elongate over the center electrodes 220a as the first and second layers.
However, the screen printing using a thermosetting electroconductive paste material or a firing type electroconductive paste material has a problems in that drooping and blurring are generated during printing, which makes it difficult to produce the center electrodes 220a to have a predetermined width.
In particular, when the center electrodes 220a and the insulation layers 230 are alternately formed, the center electrodes 220a and the insulation layers 230 are partially overlapped on the surface of the ferrite member 210, sequentially, causing the formation of concavities and convexities (step-like differences in height). For this reason, the distance between the surface of the ferrite member 210 and the screen mask becomes different, depending on positions on the screen mask. Thus, drooping or blurring tends to be generated when the center electrodes 220a as the second and third layer are printed. As a result, problems occur because it becomes difficult to obtain the center electrodes 220a having a predetermined width, or the rectangular shapes in the vertical cross-section of the center electrodes 220a become irregular, which causes the insertion loss characteristic of the center electrode assembly.
In order to overcome the problems described above, preferred embodiments of the present invention provide a center electrode assembly, a nonreciprocal circuit device of which the insertion loss is reduced and the electrical characteristics are greatly improved, a communication device, and a method of producing such a novel center electrode assembly.
According to a preferred embodiment of the present invention, a center electrode assembly includes a substrate, a plurality of center electrodes arranged so as to overlap each other at a predetermined intersecting angle each other, and insulation layers arranged between the center electrodes to insulate the center electrodes from each other, at least the center electrodes being made from a photosensitive electroconductive paste material.
Since the center electrodes are made of the photosensitive electroconductive paste material, the center electrodes having a predetermined width that can be accurately obtained by exposure using a photomask. That is, if differences in height are caused on the surface of the substrate, the center electrodes having a constant electrode width can be securely formed. Moreover, the vertical cross-sections of the center electrodes made from the photosensitive electroconductive paste material become more accurately rectangular compared to the vertical cross-sections of the center electrodes formed by screen printing using a thermosetting type electroconductive paste material or a firing (baking) type electroconductive paste material. In the case of the center electrodes having the rectangular vertical-cross-sections, the distribution of the surface current become more uniform, and the insertion loss of the center electrode assembly is greatly reduced, compared to the center electrodes having vertical cross-sections of which the edges are distorted.
The center electrodes having a width of up to approximately 150 xcexcm can be produced with high stability and accuracy, and the center electrodes having a large inductance per unit length can be obtained by using the photosensitive electroconductive paste material, since the photosensitive electroconductive paste material is used.
Regarding a high frequency current flowing through the center electrodes, the current flows in a concentrated manner in the surface portions of the center electrodes, due to the skin effect. Accordingly, the conductor loss is greatly reduced by setting the thicknesses of the center electrodes to be at least two times of the skin depth measured at the center frequency in a pass band.
Preferably, a nonreciprocal circuit device of a preferred embodiment of the present invention includes a permanent magnet, the above-described center electrode assembly to which a DC magnetic field is applied via the permanent magnet, and a metallic case which accommodates the permanent magnet and the center electrode assembly. With the above-described configuration, the insertion loss is greatly reduced. The nonreciprocal circuit device having greatly improved electrical characteristics is therefore obtained.
More preferably, the nonreciprocal circuit device further includes a mounting substrate having a matching capacitor element and a resistor element integrally formed therein, and the center electrode assembly is mounted onto the mounting substrate. Thereby, the connecting electrodes of the center electrode assembly can be simply bonded to electrodes on the mounting substrate by soldering or other suitable method. Thus, the production efficiency is greatly improved.
The communication device according to another preferred embodiment of the present invention includes the nonreciprocal circuit device having the above-described characteristics. Thus, the insertion loss is greatly reduced, and the electrical characteristics are greatly improved.
Also, the center electrode assembly having the center electrodes of which the intersecting angles are constant can be efficiently produced. Thus, the center electrode assembly, the nonreciprocal circuit device, and the communication device which achieve excellent performances and are inexpensive can be obtained.
According to another preferred embodiment of the present invention, a method of manufacturing a center electrode assembly includes the steps of coating a photosensitive electroconductive paste material onto substantially the entire main surface of a substrate, exposing, and developing the photosensitive electroconductive paste material to form a center electrode having a predetermined pattern, and coating a photosensitive insulation paste material onto substantially the entire main surface of the substrate, exposing, and developing the photosensitive insulation paste material to form an insulation layer having a predetermined pattern, the step of forming the center electrode and the step of forming the insulation layer being repeated a predetermined number of times, so that the plurality of center electrodes are arranged on the main surface of the substrate so as to form a predetermined intersecting angle with respect to each other with the insulation layers being interposed between the center electrodes.
Moreover, according to preferred embodiments of the present invention, a method of producing a center electrode assembly of the present invention includes the steps of coating a photosensitive electroconductive paste material onto substantially the entire main surface of a substrate, exposing, and developing the photosensitive electroconductive paste material to form a center electrode having a predetermined pattern, and screen-printing insulation paste onto substantially the entire main surface of the substrate, exposing, and developing the insulation paste to form an insulation layer having a predetermined pattern, the step of forming the center electrode and the step of forming the insulation layer being repeated a predetermined number of times, so that the plurality of center electrodes are arranged on the main surface of the substrate so as to form a predetermined intersecting angle with respect to each other with the insulation layers being interposed between the center electrodes.
According to the above-described methods, the center electrode assembly having the above-described characteristics can be produced with very high production efficiency.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the detailed description of preferred embodiments of the present invention with reference to the attached drawings.